Salicylic acid and benzoyl peroxide are among the most commonly used active ingredients in acne treatment due to their availability in over-the-counter products. However, many consumers do not understand the similarities and differences between them. Knowing this can help you decide which ingredient is more suitable for your skin.
Salicylic acid is a beta-hydroxy acid with exfoliating properties. It is both keratolytic and comedolytic, meaning it loosens dead skin cells and helps to break down comedones (non-inflamed clogged pores). It also has anti-inflammatory properties,[1,2] which help to treat red bumps. Since the salicylic acid molecules are lipophilic (easily dissolve into oily environments), they are able to dissolve into oily pores to perform their effects. Unfortunately, not all products containing salicylic acid will be effective since the potency of this ingredient is dependent on pH. When the pH of a formulation is too high, the salicylic acid is inactive; at pH levels that are too low (meaning the formulation is very acidic), the salicylic acid will be too irritating to the skin. Those using a product with a high concentration of salicylic acid, those with sensitive skin, or those using a poorly formulated product may experience redness, irritation, or peeling. The FDA mandates that the concentration of salicylic acid in OTC products be between 0.5-2%, and unlike benzoyl peroxide, it does not require a warning regarding sun exposure. This is because salicylic acid does not increase sensitivity to UV light, while benzoyl peroxide does.
Like salicylic acid, benzoyl peroxide is keratolytic and (mildly) comedolytic, meaning that it can clear clogged pores.[4,7] It is an excellent antibacterial agent. In fact, it is so good that there are no strains of bacteria resistant to its use. It should be used with caution, though, by those with sensitive skin as it can cause skin irritation. Benzoyl peroxide may also bleach fabrics and hair, therefore it is wise to wait until it dries on the skin before letting any clothes or hair come into contact with the skin. Products containing benzoyl peroxide will contain concentrations of either 2.5%, 5%, or 10% as regulated by the FDA.
Which concentration should you look for? Somewhat counterintuitively, the answer is the lowest concentration: 2.5%. Studies have shown that OTC products containing as little as 2.5% benzoyl peroxide will be just as effective as those with higher concentrations.[6,8] Additionally, at this concentration you will be less likely to experience the side effects of burning, peeling, redness, scaling, itching, and irritation.[6,9] Even if you do experience these adverse effects, they may be the result of an alcohol-based formulation (check to see if alcohol is one of the first two or three ingredients). If not, continual use will result in fewer side effects, although you may decide to gradually build up your frequency of use depending on the severity of the effects you experience.
Differences Between Salicylic Acid and Benzoyl Peroxide
Salicylic acid works primarily through exfoliation while benzoyl peroxide works due to its antibacterial property. Both have anti-inflammatory effects, and benzoyl peroxide can also help to exfoliate. If you have non-inflamed acne, salicylic acid may be the better choice. Conversely, if you have inflamed acne, like cystic acne, try a 2.5% benzoyl peroxide product. If you are going to use benzoyl peroxide be sure to wear sunscreen as well, even if you are only applying your treatment at night. If your acne is moderate to severe, you may need to see a physician who can treat acne using prescription medications. Early acne treatment is important in preventing acne scars and acne-related skin discoloration.